EXTERNAL CONDITIONS AND SPORE-DISCHARGE 125 



After two hours the slide was removed and examined under the 

 microscope. Any spores which had fallen upon it could be detected 

 with ease. 



The results, obtained from a number of experiments of the 

 kind just described, have served to convince me that Dmdalea 

 unicolor, Lenzites betulina, Polystictus versicolor, and P. Itirsutus 

 continue to shed their spores at the freezing point of water. 

 However, the comparatively small number of spores which settled 

 upon the glass slides each hour showed that spore-discharge is 

 not nearly so active at 0° C. as at higher temperatures. From a 

 succession of tests it was found that Lenzites hetulina continued 

 to shed its spores at 0° C. for at least three days. A fruit-body 

 of this species, whilst enclosed in the snow-chamber, set free 

 sufficient spores in a few hours to make a distinct, although faint, 

 macroscopic pattern of the gills upon a glass slide. Probably, 

 in all species which shed spores at 0° C, the discharge of spores 

 continues for an indefinite period of time until the fruit-bodies 

 become exhausted. No spore-deposit was detected as being pro- 

 duced by Schizophyllum comraune at 0° C, although spores were 

 vigorously shed by this species at 5° C. 



Ontogenetic study shows that the basidia of a hymenium come 



to maturity successively, and part with their spores as soon as 



these are ripe. The shedding of spores by Lenzites betulina, 



Diedalea unicolor, &c., in a snow-chamber indicates that in these 



fungi the development of the hymenium can still continue at 



the freezing point of water. At first, the fact that growth is 



still possible in a hymenomycetous fruit-body at 0° C, may seem 



surprising, but parallel instances of growth at this and even lower 



temperatures in other plants are by no means unknown. Thus 



in Pfeff'er's ^ list of cardinal points for growth, the minima for 



Sinapis alba (Kirchner and de Vries), Ulothrix zonata (Klebs), 



and Bacillus cyano-fuscus (Beyerinck) are given as 0° C, and on 



Arctic coasts, according to Kjellman,^ algae flourish in sea-water 



whose temperature falls to — I'S and perhaps never exceeds 0° C. 



The fruit-bodies of species of Stereum, Corticium, &c., often appear 



^ Pfeffer, Physiology of Plants, translated by A. J. Ewart, vol. ii., 1903, p. 77. 

 2 Kjellman, Bot. Zeit., 1875, p. 171. 



